Only delete from memory not from database

Question

Hi all,

I have an ActiveRecord array containing a list of shops.

shops = Shop.find(:all)

I want to delete a record from shops without deleteting it from the database.

shops.delete(a_shop) wuold result in a delete sql querry. I just want the shop to be deleted from the activerecord array but not the database.

Can this be done?

Thanks

Answer 1

I don't think you can remove the item from the array.

However, you should be able to modify your find to return the array without that shop initially. Something like:

shops = Shop.find(:all, :conditions => "id NOT #{a_shop.id}")

should be along the lines of what you want. That way you never get the shop in the container in the first place, but it doesn't affect the database.

Answer 2

When I did some testing, calling the delete method does not actually delete the element from the database. Only from the array.

shops = Shop.find(:all)
shops.delete(shops[0]) #deletes the first item from the array, not from the DB

To delete from the DB:

shops = Shop.find(:all)
Shop.delete(shops[0].id)

See the distinction? At least, this how it works on my Rails 2.1 setup.

-JP

Answer 3

Beware if you are using has_many relationship the answer by JP will not work.

Extending the example:

class City < ActiveRecord::Base
  has_many :shops
end

city = City.find(:name => "Portland")

then

city.shops.delete(city.shops[0])

Will delete from the DB!

Also

theshops = city.shops
theshops.delete(ss[0])

Will delete from the DB

One way to detach from the DB is to use compact or another array function like so:

theshops = city.shops.compact
theshops.delete(ss[0])

Will not delete from the DB

Also, in all cases delete_if Will not delete from the db:

city.shops.delete_if {|s| s.id == city.shops[0]}

Cheers!

Don't forget: If you are in doubt about these sort of things script/console is your friend!